Three-Coordinate Aluminum Alkyl Complexes for Applications in the Polymerization of Cyclic Esters

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Abstract

Bulky 1,4-diamines 1,2-[2,4,6-(CH3)3-C6H3NH-CH2]2-C6H4 and 1,2-(2,6-iPr2C6H3NHCH2)2-C6H4 were utilized as pro-ligands for the formation of novel three-coordinate aluminum alkyl compounds with the general formula [(1,4-diamido)AlR], where R = Me or Et. The synthesis of analogous aluminum hydrides was also explored resulting in the formation of four-coordinate complexes incorporating bridging hydrides.
The three-coordinate aluminum complexes were developed as single-component catalysts in the ring opening polymerization of cyclic esters. The main focus was on caprolactone polymerization, but other monomers were explored, including lactide, butyrolactone, cis-cyclooctene, and diphenylacetylene. The mechanism of polymerization with caprolactone was also studied.
The coordination chemistry of other metals and non-metals with the 1,4-diamido ligands were also investigated. Phosphorus, boron, zinc, and zirconium were the main focus. [(1,4-diamido)PCl] complexes were successfully synthesised as precursors to the formation of cationic phosphenium species, [(1,4-diamido)P]+.